A Novel Scheduling Algorithm for Densely-Deployed Wireless Stations in Urban Areas Hirozumi Yamaguchi Graduate School of IST, Osaka University Suita, Osaka, Japan Akihito Hiromori Graduate School of IST, Osaka University Suita, Osaka, Japan Teruo Higashino Graduate School of IST, Osaka University Suita, Osaka, Japan Shigeki Umehara Sumitomo Electric Industries, LTD. Osaka, Japan Hirofumi Urayama Sumitomo Electric Industries, LTD. Osaka, Japan Masaya Yamada Sumitomo Electric Industries, LTD. Osaka, Japan Taka Maeno Space-Time Engineering Japan, Inc. Tokyo, Japan Shigeru Kaneda Space-Time Engineering, LLC. Los Angeles, CA, USA Mineo Takai University of California, Los Angeles Los Angeles, CA, USA ABSTRACT This paper presents a scheduling algorithm for a set of wire- less stations such as road-side access points for vehicular net- works and outdoor WiFi stations, which are deployed in wide urban areas and may compete with each other for limited wireless resources. Different from a number of conventional approaches most of which consider detailed information on individual stations and signal interference among them, we focus more on geography of the areas of interest, and provide a novel algorithm that pursues the best balance among (i) optimality of resource utilization, (ii) robustness to new sta- tion installation and traffic demand, and (iii) scalability to the population of stations and area size. We have confirmed the performance by experimental simulations with several scenarios, and the applicability of approach has been testi- fied by a case study on a scheduling problem for roadside access points of vehicular networks in cooperation with a manufacturing corporation. Categories and Subject Descriptors C.2.1 [Computer-Communication Networks]: Network Architecture and Design—Wireless communication General Terms Algorithm, Design Keywords Resource allocation, wireless communication, scheduling Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. MSWiM’13, November 3–8, 2013, Barcelona, Spain. Copyright is held by the owner/author(s). Publication rights licensed to ACM. ACM 978-1-4503-2353-6/13/11 http://dx.doi.org/10.1145/2507924.2507939 ...$15.00. 1. INTRODUCTION Nowadays, a number of short range wireless stations are covering urban areas. For instance, outdoor public Wi-Fi access points (APs) have been deployed by AT&T, Time Warner Cable etc. to offload smartphone 3G or 4G traffic in large cities of US. In Japan, high-traffic volume in 3G cellu- lar networks is the most critical issue, and KDDI has already launched Wi-Fi services for cellular subscribers. For Intelli- gent Transport Systems (ITS), installation of DSRC (Dedi- cated Short-Range Communication) road-side units at inter- sections and on highways and city streets has been started in Japan for vehicle collision warning, local traffic information broadcast and so on. Those APs or road-side units, which we call stations hereafter, are usually densely-deployed to accommodate more clients. However, dense deployment of stations may cause severe and undesired wireless interfer- ence among them. A number of studies have been dedicated to resolve wire- less interference problems in a variety of networks such as cellular networks, wireless mesh networks (WMNs) and wire- less sensor networks (WSNs). In these approaches, schedul- ing algorithms have been proposed to reuse the wireless re- sources (either of time slots or wireless channels). That is, a channel or a time slot is concurrently used by two or more stations if they do not interfere with each other. In cellular networks, systematic resource allocation to hexagonal cells is a well-studied topic [17]. In WMNs or general wireless multi-hop networks, link scheduling is designed based on given network topology or interference graphs, and routing performance is often considered simultaneously [6]. However, most of these methods consider scheduling for individual stations and thus scalability and robustness is- sues may not be solved in urban scenarios. Firstly, it is quite expensive to gather interference information from a number of stations in city-wide areas. Therefore, some con- ventional link-based scheduling may not scale to the number of stations and size of the areas. Furthermore, some may not be robust to new station installation and traffic demand changes. Even for rapid growth of station population and traffic volume, we would like to maintain the current allo-